Well perforator



March 1966 A. A. VENGHIATTIS 3,237,706

WELL PERFORATOR 8 Sheets-Sheet 1 Filed Jan. 8, 1964 HOIST a CONTROLEQUIPMENT FIG.

FIG. Z-A FIG. 2-8

INVENTOR.

ALEXIS A. VENGHIATTIS BY ATTORNEY March 1966 A. A. VENGHlA'fTIS3,237,706

WELL PERFORATOR Filed Jan. 8, 1964 5 Sheets-Sheet 2 FIG. l-B

INVENTOR.

ALEXIS A. VENGHIATTIS ATTORNEY March 1966 A. A. VENGHIATTIS 3,237,705

WELL PERFORATOR 3 Sheets-Sheet 5 Filed Jan. 8, 1964 INVENTOR.

ALEXIS A. VENGHIATTIS FIG. 4

ATTORNEY United States Patent D 3,237,706 WELL PERFORATOP Alexis A.Venghiattis, Houston, Tex. assignor to Dresser Industries, Inc, Dailas,Tera, a corporation of Delaware Filed Jan. 8, 1964, Ser. No. 336,469 2Qlairns. (Cl. 1754.5)

This invention relates to well completion apparatus for oil and gaswells, and more particularly relates to an improved bullet perforatorfor puncturing the casing, cement and rock formation surrounding a casedborehole in the earth.

It is well known that boreholes are drilled into the earth for thepurpose of recovering oil and gas which may be trapped in subsurfacerock formations or strata. After a well has been drilled to its desireddepth, a steel casing is inserted in the well throughout its entirelength, and thereafter cement is inserted between the casing and theface of the borehole to seal off all fluid-bearing rock formations.After the casing and cement have been properly located, however, it isnecessary to puncture the casing and cement adjacent the formationsought to be tapped, in order to drain the fluids trapped in theselected formation. This technique is commonly referred to ascornpleting the well, since it is substantially the last step performedbelow the surface for obtaining a producing oil or gas well.

It has been found necessary, to obtain an adequate fluid flow, not onlyto perforate the casing and cement adjacent the selected formation, butto puncture the formation itself. Accordingly, many different means andmethods have been developed to achieve substantial penetration of therock formation, as well as penetration of the casing and cement, inorder to provide adequate passage of the fluid from the formation intothe casing. Originally, perforation was obtained solely by dischargingone or more metal bullets outwardly through the casing and cement, andinto the formations. These bullets generally achieved good penetrationof the casing and cement, but often insuflicient penetration of the morecompacted formation. Furthermore, the bullet itself would often createan obstruction to fluid flow at the point where it would lodge in theformation. Thus, well perforating apparatus was developed which employedshaped explosive charges, rather than bullets, which would provide atongue or jet of penetrating flame when exploded. This jet effectivelyburns a channel through the casing and cement and deep into theformation. Although shaped charge perforating generally achievessubstantially deeper penetration in all but the least consolidatedformations, it usually achieves such penetration without fracturing theregion about the channel. Accordingly, it has been necessary to usebullet perforators to perforate the more compacted or harder formationsbecause the fractures produced in such formations by bullets willgreatly improve the flow rates obtained in the well.

Due to the necessity for using bullet perforators, much has been done toeliminate or reduce the undesirable features of this type of Wellcompletion. It has been found that an ogivally-pointed bullet achievessubstantially greater penetration than is achieved by bullets havingrounded or comically-pointed bullets. Furthermore, it has been foundthat a sharp pointed bullet will achieve greater penetration than will ablunt-nosed bullet. However, a sharp pointed bullet all cut a smallerhole, and the tip will often break off during penetration. On the otherhand, a blunt-nosed bullet will often shatter before penetratingadequately into the formation. Consequently, the bullets presently ingeneral use in the industry are those having ogivally-pointed tips,since these bullets achieve good penetration without shattering orbreaking,

3,2317% Patented Mar. 1, 1966 and since they generally achieve at leastsome fracturing of the penetrated formations. However, ogivally-pointedbullets produce relatively small holes in the casing and formation, andtherefore it is often necessary to use larger caliber bullets, andconsequently larger propellant charges, than would otherwise benecessary.

These disadvantages of the prior art are overcome with the presentinvention, and novel bullet-type perforating apparatus is provided whichproduces a hole of a substantially greater cross-sectional area thanthat of the bullet, and which achieves greater fracturing of theformation than that achieved by bullets in present use.

Accordingly, it is an object of the present invention to provide moreeffective means for perforating a well casing in an oil or gas well.

It is also an object of the present invention to provide bulletperforation of a well casing, in a manner to produce a large holerelative to the cross section of the bullet, and at the same time toproduce good penetration and fracturing of the formation aggregate.

It is further an object of the present invention to provide an improvedbullet for use in perforating oil well casing.

It is a specific object of the present invention to provide bulletperforating apparatus wherein the bullet is of an improved design suchas to achieve good penetration into and fracturing of the formation, andalso to produce a very large hole as compared to the cross section ofthe bullet, without the necessity for employing a propelling charge ofabnormally large strength or size.

These and other objects and features of the present invention will beapparent from the following detailed description, wherein reference ismade to the accompanying drawings.

In the drawings:

FIGURE 1-A shows a pictorial representation of a gun perforatorincorporating the present invention and disposed in a well bore.

FIGURE lB shows a cross section view of the gun perforator depicted inFIGURE 1A.

FIGURE 2-A shows one view of the bullet contained in the gun perforatordepicted in FIGURES 1-A and 1-H.

FIGURE 2B shows another view of the bullet depicted in FIGURE 2-A.

FIGURE 3 depicts a cross section view of the borehole shown in FIGURE1-A after the bullet has been discharged into the earth.

FIGURE 4 depicts another view of the channel cut into the earth by thedischarged bullet shown in FIG- URE 3.

The advantages of the present invention are preferably attained by meansof gun perforating apparatus including a bullet of a novel design,wherein the tip or nose of the bullet is shaped in the manner of twoconverging planes, rather than in the manner of an ogival surface ofrevolution, and wherein the angle at which the two planes converge isselected to provide for optimum penetration without shattering orbreaking of the tip of the bullet during such penetration. As will beclearly apparent from the following description, such a bullet achievesimproved penetration of the casing as well as of the formation, andprovides for much greater flow rates from the formation through theholes in the well casing.

Referring now to FIGURE 1-A, there may be seen a cross sectional view ofa typical borehole 2 drilled into the earth 4 past at least onefluid-bearing formation 6. The borehole 2 is lined with a steel casing8, and contains cement 10 inserted in the annulus of the borehole 2 soas to seal off the formation 6. Accordingly, a conventional gunperforator 12 having a plurality of bullets 14 is lowered into thecasing 8 by means of a conventional well cable 16 until the perforator12 is at a depth which places it adjacent the formation 6 sought to betrapped.

As may be seen, the perforator 12 is suspended at one end of the cable16, and the cable 16 is supported at its other end by means of a sheavewheel 18 for connection to any suitable hoist and control equipment 20.The hoist and control equipment 20 may be of any suitable type, and istherefore depicted functionally in FIGURE 1-A.

The gun perforator 12 may be designed so as to be actuated by means ofan electrical signal from the hoist and control equipment 20, whichsignal is transmitted to the perforator 12 by means of one or moreelectrical conductors in the logging cable 16. The gun perforator 12responds to the signal by discharging a plurality of explosive charges(not shown) which serve, respectively, as propelling charges for thevarious bullets 14 carried by the gun perforator 12. In FIGURE 1-A, thebullets 14 are shown arranged in all directions about the gun perforator12. to employ a mono-directional gun perforator 12 having its bullets 14arranged linearly along the axis of the perforator 12. In either case,the explosion of the propelling charges will project the bullets 14laterally into the formation 6 in Whatever direction they may be aimedat the instant of their discharge. If the perforation is successful, atleast a substantial number of the bullets 14 will each puncture thecasing 8, and will penetrate through the cement 1t) and into theformation 6 to a substantial depth, to provide individual channelsthrough which fluids may flow from the formation 6 and into the casing8.

The gun perforator 12 comprises a generally elongated, substantiallysolid steel cylinder of sufficient strength and solidity to withstandthe explosive forces of the firing of the gun charges. Laterallydirected gun units are mounted in the cylindrical gun body atlongitudinally spaced intervals. As illustarted in FIGURE 1B, each unitcomprises an internally threaded, laterally directed barrel opening 116which receives the externally threaded barrel member 117. Preferably,the lateral depth of the barrel opening 116 and the length of the barrelmember 117 are such that the barrel member is wholly received within theopening, flush with the surface of the gun body, when fully seated andtightened therein, so as not to present any laterally projecting partswhen the gun is fully assembled in the manner shown in FIGURES 1-A andl-B.

The rear or inner end of the barrel member 117 is formed with a smooth,thread-free end 119 of slightly reduced external diameter adapted to bereceived concentrically within an inner, thread-free, counterbored endrecess 121 of the barrel opening 116. This provides a short annular endrecess between the surfaces 119 and 121 containing resilient ring 122 inorder to seal the barrel member within the barrel opening and topreclude leaking of any well fiuid inwardly from between the threadedportion of the barrel opening 116 and the external surface of the barrelmember 117.

The barrel member 117 is formed with a concentric barrel bore 123 havingat the front or muzzle end thereof a short portion of slightly enlargeddiameter forming a shallow recess 124 having an annular shoulder 126.Seated within the recess 124 and making sealing engagement against theshoulder 126, there is provided a sealing disc 127 for preventingadmission of well fluid into the barrel bore. The disc 127 may be seatedand sealed in any suitable manner well known in the art and may In somecases, however, it is desirable be formed of any suitable material, suchas brass or steel. In operation, when the propellant charge 132 isignited and the bullet 14 fired, the seal 127 is ejected from the recess124 either as a unit or in fragments and forms substantially no obstacleto the discharge of the bullet 14.

Barrel bore 123 is formed with a frusto-conical enlarged end portion 128at the inner end thereof. A

correspondingly shaped frusto-conical restraining annulus 129 fitswithin the end portion 128. A cylindrical socket 131, formed in the gunperforator 12 at the rear of the barrel opening 116, accommodates apropellant charge which comprises a compressed, molded or otherwiseconsolidated or pelletized tubular shaped body of combustible propellant132 formed with an opening 133 extending centrally therethrough from endto end. The propellant body 132 is surrounded and contained within acontainer sleeve or shell 134 which may be composed of any suitablematerial, preferably non-metallic, such as, for example, a paper orcloth-base, phenolic-impregnated tubing.

Igniter head 136 fits within the reduced diameter rear portion 137 ofsocket 131 and opening 138 in shell 134 and is positioned in closeproximity to propellant 132. Igniter head 135 forms a part ofconventional igniter 139 of the type well known in the art and may, forexample, be of the type shown and describer in US. Patent 2,649,- 736 toR. A. Phillips. Igniter 139 is actuated electrically through conductor14 1 positioned within the passage 142 and electrically connected tofiring control apparatus through the conductors of cable 16.

A bullet 14 preferably comprises a forward piercing nose portion 3preferably of the form depicted in FIG- URES 2-A and 2B and a body orrearward shank portion 32, preferably of uniform diameter extending fromthe nose portion 34 to a transverse rear end or butt 32. The bullet 14is preferably made of hardened steel or is steel jacketed in a mannerwell known in the industry to provide adequate casing and formationpiercing ability.

The bullet 14 is mounted through the annulus 129 which forms a tight,press fit therewith near the forward end of shank portion 30. The bullet14- also makes a tight, press fit within central opening formed in thecartridge cover 14-8 which is provided with a peripheral flange 14-9fitting around the forward open end of shell 13%. The fit of bullet 14-within restraining annulus 129 is preferably sufficiently tight toretard the bullet 14 until the most of the propellant 132 has beenconsumed.

Referring now to FIGURES ?.A and 2-B, respectively, there may be seentwo views of a preferred form of the bullet 14 depicted generally inFIGURE 1B, wherein the bullet 14 is shown as having a circular body withfiat butt 32 and a chisel-shaped tip 34. At the tip 34, there are twofiat surfaces 36 which are defined by two planes converging at apreselected angle. Preferably, the edge 38 of the tip 34 does notterminate in the manner of knife-edge, but is squared off substantiallyparallel with the butt 32 end of the bullet 14. The two fiat surfaces 36preferably converge at an angle which provides for optimum penetrationof the bullet 14 into the formation 6, and yet minimum probability ofbreakage of the tip 34. A suitable angle has been found to be degrees.

Referring now to FIGURES 3 and 4, there is depicted therein a pictorialrepresentation of the cased borehole shown in FIGURE 1-A, after thebullet 14 has been discharged through the cement 10 and easing 8, andafter the gun perforator 12 has been removed. Accordingly, it may beseen that, due to the shape of its nose portion 34, the bullet 14 hascarved a channel into the earth 6 which is substantially three times aswide as the diameter of the shank portion 319 of the bullet 14-. FIGURE4 shows in particular how the broad portion of the channel 41}! isperpendicular to the cutting edge 38 of the nose 36 of the bullet 14,whereas the width of the channel 40- measuring parallel with the cuttingedge 38 of the bullet 14-is only about as Wide as the diameter of thebullet 14. It is this phenomenon which amplifies the utility of thepresent invention, since the bullet 14 may be rotated appropriately inthe gun perforator 12 prior to firing, to provide for coincidence of thetilt of the channel 40 to conform with the angle of dip (or beddingplane) of the formation 6. This substantially increases the flow rate ofthe fluids which flow through the puncture 46 in the casing 8. Anotheradvantage of the bullet 14 having a nose portion 34 formed in the mannerof two converging planes, is the fact that substantial cracking orfracturing is produced in the areas of the formation 6 immediatelysurrounding the channel 40. The fissures 42 thereby produced greatlyincrease the flow rate into the channel 40, and accordingly, into thecasing 8. Furthermore, the bullet 14 itself in no way obstructs flowthrough the channel 40, as is apparent from FIGURES 3 and 4.

It may also be seen in FIGURE 4 that the channel 4%) has a crosssectional shape which tends to be a lemniscate, depending substantiallyupon the force with which the bullet 14 is projected into the formation6, and depending to some extent, perhaps, upon the angle formed bysurfaces 36 on the bullet 14. Accordingly, if the nose portion 34 of thebullet 14 be formed in the manner of a three or four sided pyramid, thenthe cross sectional shape of the channel 443 should assume a differentshape, since the enlarged portions 50 of the channel 40 appear to bedirectly related to the surfaces 36 on the nose 34 of the bullet 14.Accordingly, a bullet 14 having a nose 34 formed in the manner of twoconverging planes, i.e., formed in the manner of a chisel, appears tobest utilize the pressuring effect had on the formation 6 by the fiatsurfaces, and therefore appears to cut the best shaped channel 40insofar as flow rate is concerned.

A further advantage accruing to the chisel bullet 14 may be seen in thefact that the burrs which are produced in the puncturing of the casingare not of a character such as to obstruct fluid flow through thechannel 40. Referring to FIGURE 3, there may be seen that two largeburrs 44 are created by the bullet 14 on each side of the puncture 46 inthe casing 8, but substantially none at the top and bottom of thepuncture 46. The bottom edge 48, of the puncture 46, is indeed quiteragged. However, any burrs which originate along the bottom edge 48 (oralong the top edge) are quite small and few in number. The large burrs44 at the sides, on the other hand, seldom break loose from the casing8.

Numerous other variations and modifications may be made withoutdeparting from the scope of the present invention. Accordingly, itshould be clearly understood that the forms of the invention describedherein and shown in the figures of the accompanying drawings areillustrative only and are not intended to be construed as limitations.

What is claimed is:

1. Apparatus for perforating casing in a borehole, said apparatuscomprising a gun perforator means for discharging a bullet through saidwell casing,

a cable means for disposing said perforator means in said well casing ata preselected depth in said borehole, and

cylindrically-shaped bullet means in said gun perforator for boring ahole having a generally lemniscatelike cross sectional configurationextending through said casing and into said earth formation,

said bullet means having a cylindrical shank portion of constantdiameter and a cutting nose formed in the manner of two planesintersecting the cylindrical surface of said shank portion andconverging along the cross section diameter of said bullet.

2. Apparatus of the character described in claim 1 wherein said hole hasa cross sectional shape such that one diameter is substantially equal tothe cylindrical diameter of said bullet means and such that the otherperpendicular diameter is substantially three times as great as thecylindrical diameter of said bullet means.

References Cited by the Examiner UNITED STATES PATENTS 2,612,108 9/1952Schmidt 10252 2,806,442 9/1957 Temple 891 2,953,971 9/1960 Porter 89-13,062,294 11/1962 Huith et al 166-421 X BENJAMIN A. BORCHELT, PrimaryExaminer. SAMUEL W. ENGLE, Examiner.

1. APPARATUS FOR PERFORATING CASING IN A BOREHOLE, SAID APPARATUSCOMPRISING A GUN PERFORATOR MEANS FOR DISCHARGING A BULLET THROUGH SAIDWELL CASING, A CABLE MEANS FOR DISPOSING SAID PERFORATOR MEANS IN SAIDWELL CASING AT A PRESELECTED DEPTH IN SAID BOREHOLE, ANDCYLINDRICALLY-SHAPED BULLET MEANS IN SAID GUN PERFORATOR FOR BORING AHOLE HAVING A GENERALLY LEMNISCATELIKE CROSS SECTIONAL CONFIGURATIONEXTENDING THROUGH SAID CASING AND INTO SAID EARTH FORMATION, SAID BULLETMEANS HAVING A CYLINDRICAL SHANK PORTION OF CONSTANT DIAMETER AND ACUTTING NOSE FORMED IN THE MANNER OF TWO PLANES INTERSECTING THECYLINDRICAL SURFACE OF SAID SHANK PORTION AND CONVERGING ALONG THE CROSSSECTION DIAMETER OF SAID BULLET